Alkali and Alkaline-Earth Ion Batteries with Hexacyanometallate Cathode and Non-Metal Anode

ABSTRACT

A battery structure is provided for making alkali ion and alkaline-earth ion batteries. The battery has a hexacyanometallate cathode, a non-metal anode, and non-aqueous electrolyte. A method is provided for forming the hexacyanometallate battery cathode and non-metal battery anode prior to the battery assembly. The cathode includes hexacyanometallate particles overlying a current collector. The hexacyanometallate particles have the chemical formula A′ n , A m M1 x M2 y (CN) 6 , and have a Prussian Blue hexacyanometallate crystal structure.

RELATED APPLICATIONS

This application is a Continuation-in-Part of a pending applicationentitled, ELECTRODE FORMING PROCESS FOR METAL-ION BATTERY WITHHEXACYANOMETALLATE ELECTRODE, invented by Yuhao Lu et al., Ser. No.13/432,993, filed Mar. 28, 2012, attorney docket no. SLA3146, which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to electrochemical cells and, moreparticularly, to an alkali or alkaline-earth ion battery made from ahexacyanometallate cathode and non-metal anode.

2. Description of the Related Art

A battery is an electrochemical cell through which chemical energy andelectric energy can be converted back and forth. The energy density of abattery is determined by its voltage and charge capacity. Lithium hasthe most negative potential of −3.04 V vs. H₂/H⁺, and has the highestgravimetric capacity of 3860 milli-amp-hours per gram (mAh/g). Due totheir high energy densities, lithium-ion batteries have led the portableelectronics revolution. However, the high cost of lithium metal rendersdoubtful the commercialization of lithium batteries as large scaleenergy storage devices. Further, the demand for lithium and its reserveas a mineral have raised the need to build other types metal-ionbatteries as an alternative.

Lithium-ion (Li-ion) batteries employ lithium storage compounds as thepositive (cathode) and negative (anode) electrode materials. As abattery is cycled, lithium ions (Li⁺) exchange between the positive andnegative electrodes. Li-ion batteries have been referred to as rockingchair batteries because the lithium ions “rock” back and forth betweenthe positive and negative electrodes as the cells are charged anddischarged. The positive electrode (cathode) materials is typically ametal oxide with a layered structure, such as lithium cobalt oxide(LiCoO₂), or a material having a tunneled structure, such as lithiummanganese oxide (LiMn₂O₄), on an aluminum current collector. Thenegative electrode (anode) material is typically a graphitic carbon,also a layered material, on a copper current collector. In thecharge-discharge process, lithium ions are inserted into, or extractedfrom interstitial spaces of the active materials.

Similar to the lithium-ion batteries, metal-ion batteries use themetal-ion host compounds as their electrode materials in whichmetal-ions can move easily and reversibly. As for a Li⁺-ion, it has oneof the smallest radii of all metal ions and is compatible with theinterstitial spaces of many materials, such as the layered LiCoO₂,olivine-structured LiFePO₄, spinel-structured LiMn₂O₄, and so on. Othermetal ions, such as Na⁺, K⁺, Mg²⁺, Al³⁺, Zn²⁺, etc., with large sizes,severely distort Li-based intercalation compounds and ruin theirstructures in several charge/discharge cycles. Therefore, new materialswith large interstitial spaces would have to be used to host suchmetal-ions in a metal-ion battery.

FIG. 1 depicts the framework for an electrode material with largeinterstitial spaces in a metal-ion battery (prior art). It is inevitablethat the large interstitial spaces in these materials readily absorbwater molecules and impure ions, as shown. Water molecules also occupylattices positions in the electrode material. Although these open spacesare very suitable for the intercalation of metal-ions with large sizes,the water molecules and impure ions degrade the electrochemicalperformance. In this example, Prussian blue analogues (PBs) withcubic/tetragonal/hexagonal framework have open “zeolytic” lattices thatpermit Na⁺/K⁺-ions to move easily and reversibly in the framework.

FIG. 2 demonstrates the crystal structure of Prussian blue and itsanalogues (prior art). Their general molecular formula isAM1M2(CN)₆.zH₂O, in which tetrahedrally coordinated A site is an alkalior alkaline-earth ion, and M1 and M2 are metal ions. The M1 and M2metals are arranged in a three-dimensional checkerboard pattern, andshown in a two-dimensional pattern. The crystal structure is analogousto that of the ABX₃ perovskite. M1 and M2 metal ions are in orderedarrangement on the B sites. The M1 ions are octahedrally coordinated tothe nitrogen ends of the CN⁻ groups, and the M2 ions to their carbonends. The M1 and M2 ions are connected by the C≡N to form the Prussianblue framework with large interstitial spaces. The large interstitialsites may host the large sized alkali or alkaline-earth ions (A). Watermolecules may also occupy lattice positions in the PB analogues. The ionchannels connecting the interstitial sites are similar in size tosolvated alkali ions such as sodium, potassium, and alkaline-earth ionssuch as magnesium and calcium allowing rapid transport of these ionsthroughout the lattice. Therefore, PB is a good choice for an electrodematerial in sodium/potassium/magnesium/calcium-ion batteries.Nonetheless, thermogravimetric analysis (TG) suggests that every PBmolecule contains four to six water molecules. The occupation of waterand impure ions in these materials definitely reduces the spaces to hostthe metal-ions and leads to the reduced capacity of these electrodematerials. Therefore, KCuFe(CN)₆ has a theoretical capacity of 85.2mAh/g, but its practical capacity is smaller than 60 mAh/g. In addition,water may react with the intercalated metal-ions and decrease thecoulombic and energy efficiencies of the metal-ion batteries. Up to now,no method is reported to remove the water and impure ions from the largeinterstitial spaces and lattice positions of the hexacyanometallateelectrode materials for metal-ions batteries. As a result, mostmetal-ions batteries with a hexacyanometallate electrode use an aqueoussolution as an electrolyte. These batteries have small specificcapacities and low voltages.

The open framework structure of the transition metal hexacyanometallatesoffers faster and reversible intercalation process for alkali andalkaline-earth ions (A_(x)). In a metal-ion battery structure, the metalions need to be stored in either anode or cathode electrode beforeassembly. In the case of a Li-ion battery with LiCoO₂, LiFePO₄, andLiMn₂O₄ cathodes, the Li ions are stored in the cathode and the anode iscarbon. Therefore, these batteries are assembled in a discharged state.These batteries need to be run through a charge cycle, to move the Liions to the carbon anode, before they have any power for discharge. Inthe case of Li—S, Li-air and Na—S batteries, the metal ions are storedin anode. Actually, these anodes are made of Li and Na metals. Thesebatteries are assembled in the charged state—meaning the battery candischarge immediately after assembly. Since alkali (e.g., Li, Na, andK), and other alkaline-earth (e.g., Mg and Ca) metals are very reactivewith water vapor and oxygen, the manufacturing cost for such a batterywould be prohibitively high, as the manufacturing has to be done incontrolled environment.

In the case of sodium-ion batteries and potassium-ion batteries withhexacyanometallates A_(x)M₁M₂(CN)₆ as the cathode materials, it is easyto use a metal anode for the metal-ion battery. For example, a Na-ionbattery can be made of a sodium anode and KFe₂(CN)₆ cathode, or a K-ionbattery with potassium anode and KFe₂(CN)₆ cathode. However, thesebatteries must be assembled in controlled environment (H₂O-free,oxygen-free) if a metal anode is used.

It would be advantageous if alkali and alkaline-earth ion batteriescould be made with a hexacyanometallate A_(x)M₁M₂(CN)₆ cathode and anon-metal anode.

SUMMARY OF THE INVENTION

Described herein is an alkali-ion battery (e.g., a sodium-ion battery orpotassium-ion battery) with a cathode of A_(x)M₁M₂(CN)₆, where the Acations may be Na or K, for example, where x=0-2 and the anode is anon-metal. Also disclosed is an alkaline-earth-ion battery (e.g., amagnesium-ion battery or calcium-ion battery) with a cathode ofA_(x)M₁M₂(CN)₆, where the A cations are Mg or Ca, for example, wherex=0-1 and the anode is a non-metal. The non-metal materials for thenegative electrode (anode) include carbonaceous materials, oxides,sulfide, and so on.

The battery demonstrates high energy, long cycling life and low cost.Also disclosed is a process of forming an electrode that acts as anion-source for hexacyanometallates, initially without sodium orpotassium ions. A non-aqueous, polymer, or solid electrolyte can be usedin the battery. M₁ and M₂ are the same or different metal ions. Someexamples of M₁ and M₂ are as follows: M₁, M₂=Ti, V, Cr, Mn, Fe, Co Ni,Cu, Zn, Ca, Mg, etc. The ratio of M₁ and M₂ can be an arbitrary number.The battery demonstrates a high voltage due to the use of a non-aqueouselectrolyte. Accordingly, a method is provided for forming ahexacyanometallate battery cathode. The method provides driedhexacyanometallate particles having a chemical formulaA′_(n)M1_(x)M2_(y)(CN)₆ with a Prussian Blue hexacyanometallate crystalstructure, including impurities and H₂O. A′ is an alkali oralkaline-earth cation. M1 is a metal with 2+ or 3+ valance positions.Likewise, M2 is a metal with 2+ or 3+ valance positions. (n) is in therange of 0.5 to 2, x is in the range of 0.5 to 1.5, and y is in therange of 0.5 to 1.5. The hexacyanometallate particles are mixed with abinder and electronic conductor powder in a low boiling point solvent.Drying the mixture forms a A′_(n)M1_(x)M2_(y)(CN)₆ paste. A metalcurrent collector is coated with the paste, forming a cathode. Afterdrying the paste, the cathode is soaked in an organic first electrolyteincluding a salt with alkali or alkaline-earth cations, and a firstelectric field is created in the first electrolyte between the cathodeand a first counter electrode. In response to the first electric field,the method simultaneously removes A′ cations, impurities, and watermolecules from interstitial spaces and lattice positions in the PrussianBlue hexacyanometallate crystal structure. Hexacyanometallate particles,having a chemical formula of A′_(n),M1_(x)M2_(y)(CN)₆, where n′<n, areformed overlying the cathode.

The method then soaks the cathode in an organic second electrolyteincluding a salt with A cations, where A is an alkali or alkaline-earthcation. In response to creating a second electric field in the secondelectrolyte between the cathode and a second counter electrode includingA elements, A cations are added into the interstitial spaces of theA′_(n),M1_(x)M2_(y)(CN)₆ crystal structure. As a result, a cathode isformed with hexacyanometallate particles having the chemical formulaA′_(n),M1_(x)M2_(y)(CN)₆, where m is in a range of 0.5 to 2.

Additional details of the above-described method and a battery with ahexacyanometallate cathode and non-metal anode are presented below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts the framework for an electrode material with largeinterstitial spaces in a metal-ion battery (prior art).

FIG. 2 demonstrates the crystal structure of Prussian blue and itsanalogues (prior art).

FIG. 3 is a partial cross-sectional view of a battery with ahexacyanometallate cathode and non-metal anode.

FIG. 4 is a partial cross-sectional schematic view of a Na-ion batteryin the discharge state, with a Na_(x)M₁M₂(CN)₆ positive electrode and anon-metal negative electrode separated by a Nat-ion permeable membrane.

FIGS. 5A through 5C depict three types of battery configurations.

FIG. 6 is a flowchart illustrating a method for forming ahexacyanometallate battery cathode.

FIG. 7 is a flowchart illustrating a method for forming a non-metalbattery anode.

DETAILED DESCRIPTION

FIG. 3 is a partial cross-sectional view of a battery with ahexacyanometallate cathode and non-metal anode. The battery 100comprises a cathode 102 with hexacyanometallate particles 104 overlyinga current collector 106. The hexacyanometallate particles 104 have thechemical formula A′_(n),M1_(x)M2_(y)(CN)₆, and have a Prussian Bluehexacyanometallate crystal structure (see FIG. 2). The A cations may beeither alkali or alkaline-earth cations. Likewise, the A′ cations may beeither alkali or alkaline-earth cations. For example, the A and A′cations may be Na⁺, K⁺, Mg²⁺, or Ca²⁺. Note: the A and A′ cations may bethe same or a different material.

M1 is a metal with 2+or 3+valance positions. Likewise, M2 is a metalwith 2+ or 3+ valance positions. For example, the M1 and M2 metals maybe Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ca, or Mg. The M1 metal may be thesame metal as the M2 metal, or a different metal than the M2 metal.

From the hexacyanometallate formula above, m is in the range of 0.5 to2, x is in the range of 0.5 to 1.5, y is in the range of 0.5 to 1.5, andn′ is in the range of 0 to 2. In one aspect, the cathodehexacyanometallate particles 104 have the chemical formula A_(m)M1_(x)M₂_(y)(CN)₆, where n′=0.

The battery 100 further comprises an electrolyte 108 capable ofconducting A cations 110. An ion-permeable membrane 112 separates anon-metal anode 114 from the cathode 102. Some examples of anodematerials include carbonaceous materials, oxides, sulfides, nitrides,silicon, composite material including metal nanoparticles withcarbonaceous materials, and silicon nanostructures with carbonaceousmaterials. The electrolyte 108 may be a non-aqueous, organic, gel,polymer, solid electrolyte, or aqueous electrolyte.

In one example of the battery, the A cations are Na cations, the ionpermeable membrane 112 is a Na⁺-ion permeable membrane, and theelectrolyte 108 is a Na⁺ soluble non-aqueous electrolyte. The generalexpression for the cathode may be: Na₂M₁M₂(CN)₆, NaM₁M₂(CN)₆,NaKM₁M₂(CN)₆, or M₁M₂(CN)₆. M₁, M₂=Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn,Ca, Mg, etc. The ratio of M₁ and M2 can be an arbitrary number. Forexample: Na₂Fe₂(CN)₆, NaFe₂(CN)₆, NaKFe₂(CN)₆, and Fe₂(CN)₆.

In another example, the A cations are K+cations, the ion permeablemembrane 112 is a K⁺-ion permeable membrane, and the electrolyte 108 isa K⁺ soluble non-aqueous electrolyte. The general expression for thecathode materials may be: K₂M₁M₂(CN)₆, KM₁M₂(CN)₆, NaKM₁M₂(CN)₆, orM₁M₂(CN)₆. M₁, M₂=Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ca, Mg, etc. Theratio of M₁ and M₂ can be an arbitrary number. For example: K₂Fe₂(CN)₆,KFe₂(CN)₆, and NaKFe₂(CN)₆.

In another example, the A cations are Mg²⁺ cations, the ion permeablemembrane 112 is a Mg²⁺-ion permeable membrane, and the electrolyte 108is a Mg²⁺ soluble non-aqueous electrolyte. The general expression forthe cathode materials may be: MgM₁M₂(CN)₆, Mg_(0.5)M₁M₂(CN)₆, orM₁M₂(CN)₆. M₁, M₂=Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ca, Mg, etc. Theratio of M₁ and M₂ can be an arbitrary number. For example: MgFe₂(CN)₆,Mg_(0.5)Fe₂(CN)₆, or Fe₂(CN)₆.

If the A cations are Ca²⁺ cations, the ion permeable membrane 112 is aCa²⁺-ion permeable membrane, and the electrolyte 108 is a Ca²⁺ solublenon-aqueous electrolyte. The general expression for the Ca-ion batteryis the same as the Mg-ion battery, just replacing Mg with Ca in theformulas above.

In one aspect, the cathode hexacyanometallate particles 104 have thechemical formula A′_(n),M1_(x)M2_(y)(CN)₆, where m=0. The anode 114includes A cations, and the ion-permeable membrane 112 is permeable to Acations. More explicitly, the ion-permeable membrane 112 is permeable tothe A cations used in the anode 114. As used herein, an anode is definedas being a non-metal anode if it is a composite material that includes ametal.

Thus, sodium-ion, potassium-ion, magnesium-ion, and calcium-ionbatteries are disclosed with positive (cathode) electrodes ofA_(x)M₁M₂(CN)₆, negative (anode) electrodes of a non-metal material, anion-permeable membrane separating the cathode and anode, and anelectrolyte. The material, A_(x)M₁M₂(CN)₆, demonstrates a framework thatconsists of a M₁-N—C-M₂ skeleton and large interstitial space as shownin FIG. 2. M₁ and M₂ are the same or different metal ions (M₁, M₂=Ti, V,Cr, Mn, Fe, Co, Ni, Cu, Zn, Ca, Mg, etc.) and their ratio can be anarbitrary number. A-ions (Na, K, Mg and Ca) can easily and reversiblymove in the interstitial space. The anode is a non-metal material. Itcan be one of carbonaceous materials, oxides, sulfides or nitrides. Inorder to obtain a high voltage for the battery, a non-aqueouselectrolyte, such as organic electrolyte, gel electrolyte, polymerelectrolyte, solid electrolyte, etc., may be used in the battery.

FIG. 4 is a partial cross-sectional schematic view of a Na-ion batteryin the discharge state, with a Na_(x)M₁M₂(CN)₆ positive electrode 102and a non-metal negative electrode 114 separated by a Na⁺-ion permeablemembrane 112. In order to obtain a high voltage, a Na solublenon-aqueous solution 108, polymer, or solid electrolyte is used in theNa-ion battery. The non-metal negative electrode 114 is the carbonaceousmaterial, oxide, sulfide, and so on. In the charge/discharge process,Na⁺ ions “rock” back and forth between the positive electrode 102 andnegative electrode 114. Similarly, a K-ion battery would have ofK_(x)M₁M₂(CN)₆ positive electrode, a non-metal negative electrode, and aK⁺-ion permeable membrane separating the cathode and anode electrodes.The battery charge reactions at the cathode and anode are shown below.

-   -   For sodium-ion battery, the positive electrode:

Na_(x)M₁M₂(CN)₆→xNa⁺+M₁M₂(CN)₆+xe⁻; and,

-   -   the negative electrode:

Na⁺ e ⁻+□→(Na) □; ␣=non-metal negative electrode material.

-   -   For potassium-ion battery, the positive electrode:    -   K_(x)M₁M₂(CN)₆→xK⁺+M₁M₂(CN)₆+xe⁻; and,    -   the negative electrode:

K⁺ +e ⁻+□→(K) □; ␣=non-metal negative electrode material.

-   -   For magnesium-ion battery, the positive electrode:

Mg_(x)M₁M₂(CN)₆→xMg²⁺+M₁M₂(CN)₆+2xe⁻; and,

-   -   the negative electrode:

Mg²⁺+2e ⁻+□→(Mg) □; □=non-metal negative electrode material.

-   -   For calcium-ion battery, the positive electrode:

Ca_(x)M₁M₂(CN)₆→xCa²⁺+M₁M₂(CN)₆+2xe⁻; and,

-   -   the negative electrode:

Ca²⁺+2e ⁻+□→(Ca) □; □=non-metal negative electrode material.

In the discharge process, all reactions take place in the reversedirection.

The positive electrode fabrication process flow is as follows. DriedA′_(n)M₁M₂(CN)₆ (A′=Na, K, Mg, or Ca) powder with a particle size of 5nm-1 μm is mixed with binder, such as polytetrafluoroethylene (PTFE),polyvinylidene fluoride (PVDF), etc., and an electronic conductorpowder, in a low boiling point solvent to form a paste. The electronicconductor powder may be carbon black, carbon nanotube, carbon nanowire,grapheme, etc., with particle size of 5 nm-10 μm. The A′_(n)M₁M₂(CN)₆(A′=Na, K, Mg, or Ca) powder contains crystal water even after thedrying process. The water is not shown in the formula. The compositionof the paste is 60 wt. %-95 wt. % A′_(n)M₁M₂(CN)₆, 0 wt. %-30 wt. %electronic conductor powder, and 1 wt. %-15 wt. % binder. The paste iscoated on a metal foil or mesh (Al, Ti, etc.) that is used as thecurrent collector for the positive electrode. After drying, theelectrode undergoes forming process. The forming process includes twosteps: the first step is to remove the ions (A′_(n)) and residual waterfrom the A′_(n)M₁M₂(CN)₆ lattice. The second step is to fill Na-ions,K-ions, Mg-ions, or Ca-ions into the A′_(n)M₁M₂(CN)₆ lattice. The Naions and K ions (Mg ions and Ca ions) occupy the A site and these ionsare moved in/out of the A′_(n)A_(m)M₁M₂(CN)₆ lattice during thedischarge/charge cycles. Additional details of the 2-step formingprocess are provided in parent application entitled, ELECTRODE FORMINGPROCESS FOR METAL-ION BATTERY WITH HEXACYANOMETALLATE ELECTRODE,invented by Yuhao Lu et al., Ser. No. 13/432,993.

The forming process can be summarized as follows. For simplicity, it isassumed that the ions at the A site are all removed in the first step.

In the first step:

A′_(n)M₁M₂(CN)₆=nA′+M₁M₂(CN)₆+ne⁻;

Residual water is removed: 2H₂O=4H⁺+O₂→+4e ⁻.

In the second step:

M ₁ M ₂(CN)₆ +me ⁻ +mNa⁺→Na_(m) M ₁ M ₂(CN)₆(m≧1) for the sodium-ionbattery; or,

M ₁ M ₂(CN)₆ +me ⁻ +mK⁺→K_(m) M ₁ M ₂(CN)₆(m≧1) for the potassium-ionbattery; or,

M ₁ M ₂(CN)₆+2me ⁻ +mMg²⁺→Mg_(m) M ₁ M ₂(CN)₆(m≧0.5) for themagnesium-ion battery; or,

M ₁ M ₂(CN)₆+2me ⁻ +mCa²⁺→Ca_(m) M ₁ M ₂(CN)₆(m≧0.5) for the calcium-ionbattery.

All steps are operated in a water-free environment. After the formingprocess, the electrode is ready for battery assembly.

Note that the A′ ions in cathode material A′_(n)M₁M₂(CN)₆ before theforming process, and the A ions in A_(m)M₁M₂(CN)₆ after forming processmay be a different material. For example, K_(x)M₁M₂(CN)₆ is used beforethe electrode forming process, and the materials change toNa_(x)M₁M₂(CN)₆ or Na_(x)K_(y)M₁M₂(CN)₆ after forming process for aNa-ion battery application.

The negative (anode) electrode is fabricated as follows. A driednon-metal negative electrode powder (e.g., carbonaceous material,oxides, or sulfides) is mixed with binder such as PTFE or PVDF, etc.,and an electronic conductor powder (carbon black, carbon nanotube,carbon nanowire, grapheme, etc., with particle size of 5 nm-10 μm) inlow boiling point solvent to form a paste. The composition of the pasteis 60 wt. %-95 wt. % non-metal anode, 0 wt. %-30 wt. % electronicconductor powder, and 1 wt. %-15 wt. % binder. The paste is coated on ametal foil or mesh (Cu, Ti, Ni, etc.) that is used as the currentcollector for the negative electrode. The negative electrode has a verylow potential that can reduce the organic electrolyte to form anion-permeable layer on the negative electrode so-called solidelectrolyte interphase (SEI). The SEI improves the stability of thenegative electrode in the ion battery. However, the reduction reactionexhausts the metal-ions (Na⁺, K⁺, Mg²⁺, or Ca²⁺) from the positiveelectrode, which decreases the capacity of the positive electrode. So aprocess of forming the electrode is applied to the negative electrodeprior to the electrode slitting and battery assembly. The formingprocess is performed in a water-free environment. The negative electrode(anode) is paired with a counter metal-electrode (e.g., Na, K, Mg, Ca)in an electrochemical cell that includes an organic electrolyte withmetal-ions (Na⁺, K⁺, Mg²⁺, Ca²⁺). Upon receiving the electrical field inthe electrochemical cell that moves the metal ions toward the negativeelectrode, the metal-ions insert into or react with the negativeelectrode. At the same time, the electrolyte reacts with the negativeelectrode to form a SEI layer that contains metal ions, carbon, oxygen,and hydrogen on the negative electrode surface. Next, in the sameelectrochemical cell, an opposite electrical field is applied and themetal-ions are de-inserted from the negative electrode. However, the SEIlayer is intact. For example, if a Na-ion battery is being formed, thecounter electrode in made with Na, and the electrolyte includes Na ions.After the process, an-ion permeable inner layer forms on the electrode.

FIGS. 5A through 5C depict three types of battery configurations. Afterthe positive electrode and the negative electrode are prepared, thebattery can be assembled. A membrane separates the positive and negativeelectrode. The membrane can be one of polymer, gel, or solid materials.The sandwich electrode assembly can be configured according to thecontainer shape of the battery. The electrode assembly is put into acontainer. If a liquid solution is needed to help the ion transport, itcan be injected into the container. After all the electrodes arethoroughly soaked in electrolyte, the container is sealed.

An all-solid sodium ion-battery or potassium-ion battery, uses adifferent composition for the electrode fabrication. The all-solid ionbattery consists of the positive electrode and the negative electrodeseparated by an ion-conduct solid electrolyte. For example, in thesodium-ion battery, β-Al₂O₃, NaZr₂(PO₄)₃, Na₄Zr₂(SiO₄)₃ and theirderivates can be used as the Nat-ion solid electrolyte. In order toimprove the ions transport in the electrode, the 5 wt. %-60 wt. % solidelectrolyte powder can be added into the pastes of the positiveelectrode and the negative electrode to prepare the electrode. Afterobtaining the electrode, they can be assembled into a battery asdescribed above.

FIG. 6 is a flowchart illustrating a method for forming ahexacyanometallate battery cathode. Although the method is depicted as asequence of numbered steps for clarity, the numbering does notnecessarily dictate the order of the steps. It should be understood thatsome of these steps may be skipped, performed in parallel, or performedwithout the requirement of maintaining a strict order of sequence.Generally however, the method follows the numeric order of the depictedsteps. The method starts at Step 600.

Step 602 provides dried hexacyanometallate particles having a chemicalformula A′_(n)M1_(x)M2_(y)(CN)₆ with a Prussian Blue hexacyanometallatecrystal structure, including impurities and H₂O. A′ is either an alkalior alkaline-earth cations, and M1 is a metal with 2+ or 3+ valancepositions. Likewise, M2 is a metal 2+ or 3+ valance positions, n is inthe range of 0.5 to 2, x is in the range of 0.5 to 1.5, and y is in therange of 0.5 to 1.5. For example, the A′ cations may be Na⁺, K⁺, Mg²⁺,or Ca²⁺. The M1 metal may be Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ca, orMg for example. Likewise, the M2 metal may be Ti, V, Cr, Mn, Fe, Co, Ni,Cu, Zn, Ca, or Mg. The M1 may be the same metal as the M2 metal or adifferent metal than the M2 metal. The dried hexacyanometallateparticles typically have a size in the range of 5 nm to 10 microns.

Step 604 mixes the hexacyanometallate particles with a binder andelectronic conductor powder in a low boiling point solvent.

Some examples of low boiling point solvents include amyl acetate,acetone, diethyl carbonate, dimethyl carbonate, andn-methyl-2-pyrrolidone (NMP). The binder may be PTFE or PVDF, forexample. Typically, the electronic conductor powder is carbon black,carbon nanotubes, carbon nanowire, or grapheme, having a particle sizein the range of 5 nm to 10 microns.

Step 606 dries the mixture, forming a A′_(n)M1_(x)M2_(y)(CN)₆ paste. Inone aspect, the paste is 60 to 95 weight (wt) % A′_(n)M1_(x)M2_(y)(CN)₆,0 to 30 wt % electronic conductor powder, and 1 to 15 wt % binder.

Step 608 coats a metal current collector with the paste, forming acathode. Step 610 dries the paste. Step 612 soaks the cathode in anorganic first electrolyte including a salt with either alkali oralkaline-earth cations. Step 614 accepts a first electric field in thefirst electrolyte between the cathode and a first counter electrode. Inresponse to the first electric field, Step 616 simultaneously removes A′cations, impurities, and water molecules from interstitial spaces in thePrussian Blue hexacyanometallate crystal structure. Step 618 formshexacyanometallate particles having a chemical formula ofA′_(n),M1_(x)M2_(y)(CN)₆, where n′<n, overlying the cathode.

In one aspect, subsequent to forming A′_(n),M1_(x)M2_(y)(CN)₆ in Step618, Step 620 soaks the cathode in an organic second electrolyteincluding a salt with A cations, where A is either an alkali oralkaline-earth cation. Typically, the A cations are Na⁺, K⁺, Mg²⁺, orCa²⁺. The A cations may be the same material as the A′ cations or adifferent material than the A′ cations.

Step 622 accepts a second electric field in the second electrolytebetween the cathode and a second counter electrode including A elements.In response to the second electric field, Step 624 adds A cations intothe interstitial spaces of the A′_(n),M1_(x)M2_(y)(CN)₆ crystalstructure. Step 626 forms a cathode with hexacyanometallate particleshaving the chemical formula A′_(n),A_(m)M1xM2y(CN)₆, where m is in arange of 0.5 to 2. In one aspect, Step 626 forms hexacyanometallateparticles with the chemical formula of A_(m)M1_(x)M2_(y)(CN)₆, wheren′=0.

FIG. 7 is a flowchart illustrating a method for forming a non-metalbattery anode. The method begins at Step 700. Step 702 provides a driednon-metal electrode powder. Step 704 mixes the dried non-metal electrodepowder with a binder and an electronic conductor powder in a low boilingpoint solvent. Step 706 forms a paste. Step 708 coats a metal currentcollector with the paste, forming an anode. In Step 710 the paste dries.Step 712 soaks the anode in a first organic electrolyte including a saltwith metal ions. Step 714 accepts a first electric field in theelectrolyte between the anode and a metal first counter electrode. Inresponse to the first electric field, Step 716 forms a metal solidelectrolyte interphase (SEI) layer overlying the anode. In one aspect,the metal SEI layer additionally includes carbon, oxygen, hydrogen, andcombinations of the above-mentioned elements.

Subsequent to forming the SEI layer, Step 718 accepts a second electricfield, opposite in polarity to the first electric field between theanode and the first counter electrode. Step 720 removes metal ions fromthe anode while maintaining the SEI layers intact.

In one aspect, soaking the anode in the first organic electrolyte inStep 712 includes soaking in a first organic electrolyte with A cationssuch as Na, K, Mg, or Ca. Likewise, Step 714 uses a metal first counterelectrode that additional includes the A cations used in Step 712. Then,Step 716 forms the anode from a composite that includes the A cationsused in Steps 712 and 714.

A battery with a hexacyanometallate cathode and non-metal anode has beenprovided with an associated cathode fabrication process. Examples ofparticular materials and process steps have been presented to illustratethe invention. However, the invention is not limited to merely theseexamples. Other variations and embodiments of the invention will occurto those skilled in the art.

We claim:
 1. A battery with a hexacyanometallate cathode and non-metalanode, the battery comprising: a cathode with hexacyanometallateparticles overlying a current collector, the hexacyanometallateparticles having a chemical formula A′_(n),A_(m)M1_(x)M2_(y)(CN)₆, andhaving a Prussian Blue hexacyanometallate crystal structure, where Acations are selected from a group consisting of alkali andalkaline-earth cations; where A′ cations are selected from a groupconsisting of alkali and alkaline-earth cations; where M1 is a metalselected from a group consisting of 2+ and 3+ valance positions; whereM2 is a metal selected from a group consisting of 2+ and 3+ valancepositions; where m is in a range of 0.5 to 2; where x is in a range of0.5 to 1.5; where y is in a range of 0.5 to 1.5; where n′ is in a rangeof 0 to 2; an electrolyte capable of conducting A cations; a non-metalanode; and, an ion-permeable membrane separating the anode from thecathode.
 2. The battery of claim 1 wherein A cations are selected from afirst group consisting of Na⁺, K⁺, Mg²⁺, and Ca²⁺; and, wherein A′cations are selected from a first group consisting of Na⁺, K⁺, Mg²⁺, andCa²⁺.
 3. The battery of claim 1 wherein the M1 metal is selected from agroup consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ca, and Mg; and,wherein the M2 metal is selected from a group consisting of Ti, V, Cr,Mn, Fe, Co, Ni, Cu, Zn, Ca, and Mg.
 4. The battery of claim 1 whereinthe M1 metal is selected from a group consisting of the same metal asthe M2 metal and a different metal than the M2 metal.
 5. The battery ofclaim 1 wherein the anode material is selected from a group consistingof carbonaceous materials, oxides, sulfides, nitrides, silicon,composite material including metal nanoparticles with carbonaceousmaterials, and silicon nanostructures with carbonaceous materials. 6.The battery of claim 1 wherein the electrolyte is selected from a groupconsisting of non-aqueous, organic, gel, polymer, solid electrolyte, andaqueous electrolytes.
 7. The battery of claim 1 wherein the A cationsare Na⁺ cations; wherein the ion permeable membrane is a Nat-ionpermeable membrane; and, wherein the electrolyte is a Na⁺ solublenon-aqueous electrolyte.
 8. The battery of claim 1 wherein the A cationsare K⁺ cations; wherein the ion permeable membrane is a K⁺-ion permeablemembrane; and, wherein the electrolyte is a K⁺ soluble non-aqueouselectrolyte.
 9. The battery of claim 1 wherein the A cations are Mg²⁺cations; wherein the ion permeable membrane is a Mg²⁺-ion permeablemembrane; and, wherein the electrolyte is a Mg²⁺ soluble non-aqueouselectrolyte.
 10. The battery of claim 1 wherein the A cations are Ca²⁺cations; wherein the ion permeable membrane is a Ca²⁺-ion permeablemembrane; and, wherein the electrolyte is a Ca²⁺ soluble non-aqueouselectrolyte.
 11. The battery of claim 1 wherein A cations are selectedfrom a group consisting of the same material as the A′ cations and adifferent material than the A′ cations.
 12. The battery of claim 1wherein the cathode hexacyanometallate particles have the chemicalformula A_(m)M1_(x)M2_(y)(CN)₆, where n′=0.
 13. The battery of claim 1wherein the cathode hexacyanometallate particles have the chemicalformula A′_(n),M1_(x)M2_(y)(CN)₆, where m=0; wherein the anode includesA cations; and, wherein the ion-permeable membrane is permeable to Acations.
 14. A method for forming a hexacyanometallate battery cathode,the method comprising: providing dried hexacyanometallate particleshaving a chemical formula A′_(m)M1_(x)M2_(y)(CN)₆ with a Prussian Bluehexacyanometallate crystal structure, including impurities and H₂O;where A′ is selected from a group consisting of alkali andalkaline-earth cations; where M1 is a metal selected from a groupconsisting of 2+ and 3+ valance positions; where M2 is a metal selectedfrom a group consisting of 2+ and 3+ valance positions; where n is in arange of 0.5 to 2; where x is in a range of 0.5 to 1.5; where y is in arange of 0.5 to 1.5; mixing the hexacyanometallate particles with abinder and electronic conductor powder in a low boiling point solvent;drying the mixture, forming a A′hd nM1_(x)M2_(y)(CN)₆ paste; coating ametal current collector with the paste, forming a cathode; drying thepaste; soaking the cathode in an organic first electrolyte including asalt selected from the group consisting of alkali and alkaline-earthcations; accepting a first electric field in the first electrolytebetween the cathode and a first counter electrode; in response to thefirst electric field, simultaneously removing A′ cations, impurities,and water molecules from interstitial spaces in the Prussian Bluehexacyanometallate crystal structure; and, forming hexacyanometallateparticles having a chemical formula of A′_(n),M1_(x)M2_(y)(CN)₆, wheren′<n, overlying the cathode.
 15. The method of claim 14 furthercomprising: subsequent to forming A′_(n),M1_(x)M2_(y)(CN)₆, soaking thecathode in an organic second electrolyte including a salt with Acations, where A is selected from a group consisting of alkali andalkaline-earth cations; accepting a second electric field in the secondelectrolyte between the cathode and a second counter electrode includingA elements; in response to the second electric field, adding A cationsinto the interstitial spaces of the A′_(n),M1_(x)M2_(y)(CN)₆ crystalstructure; and, forming a cathode with hexacyanometallate particleshaving the chemical formula A′_(n),A_(m)M1_(x)M2_(y)(CN)₆, where m is ina range of 0.5 to
 2. 16. The method of claim 15 wherein soaking thecathode in the second electrolyte including a salt with A cationsincludes the A cations being selected from a group consisting the samematerial as the A′ cations and a different material than the A′ cations.17. The method of claim 14 wherein the A′ cations are selected from agroup consisting of Na⁺, K⁺, Mg²⁺, and Ca²⁺.
 18. The method of claim 15wherein the A cations are selected from a group consisting of Na⁺, K⁺,Mg²⁺, and Ca²⁺.
 19. The method of claim 14 wherein the M1 metal isselected from a group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn,Ca, and Mg; and, wherein the M2 metal is selected from a groupconsisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ca, and Mg.
 20. Themethod of claim 14 wherein the M1 metal is selected from a groupconsisting of the same metal as the M2 metal and a different metal thanthe M2 metal.
 21. The method of claim 14 wherein providing the driedhexacyanometallate particles includes providing particles having a sizein a range of 5 nanometers (nm) to 10 microns.
 22. The method of claim14 wherein mixing the hexacyanometallate particles with the binder andelectronic conductor powder includes mixing with a binder selected froma group consisting of polytetrafluoroethylene (PTFE) and PVDF.
 23. Themethod of claim 14 wherein mixing the hexacyanometallate particles withthe binder and electronic conductor powder includes mixing with anelectronic conductor powder selected from a group consisting of carbonblack, carbon nanotubes, carbon nanowire, and grapheme, having aparticle size in a range of 5 nm to 10 microns.
 24. The method of claim14 wherein forming the A′_(n)M1_(x)M2_(y)(CN)₆ paste includes forming apaste with 60 to 95 weight (wt) % A′_(n)M1_(x)M2_(y)(CN)₆, 0 to 30 wt %electronic conductor powder, and 1 to 15 wt % binder.
 25. The method ofclaim 15 wherein forming hexacyanometallate particles having a chemicalformula of A_(m)A′_(n),M1_(x)M2_(y)(CN)₆ includes forminghexacyanometallate particles with the chemical formula ofA_(m)M1_(x)M2_(y)(CN)₆, where n′=0.
 26. A method for forming a non-metalbattery anode, the method comprising: providing a dried non-metalelectrode powder; mixing the dried non-metal electrode powder with abinder and an electronic conductor powder in a low boiling pointsolvent; forming a paste; coating a metal current collector with thepaste, forming an anode; drying the paste; soaking the anode in a firstorganic electrolyte including a salt with metal ions; accepting a firstelectric field in the electrolyte between the anode and a metal firstcounter electrode; and, in response to the first electric field, forminga metal solid electrolyte interphase (SEI) layer overlying the anode.27. The method of claim 26 further comprising: subsequent to forming theSEI layer, accepting a second electric field, opposite in polarity tothe first electric field between the anode and the first counterelectrode; and, removing metal ions from the anode while maintaining theSEI layers intact.
 28. The method of claim 26 wherein soaking the anodein the first organic electrolyte includes the metal ions being selectedfrom a group consisting of Na, K, Mg, and Ca; and, wherein accepting thefirst electric field includes accepting the electrolyte between theanode and a first counter electrode with the selected metal ions. 29.The method of claim 26 wherein forming the metal SEI layer overlying theanode includes forming an SEI with additional elements selected from agroup consisting of carbon, oxygen, hydrogen, and combinations of theabove-mentioned elements.
 30. The method of claim 26 wherein soaking theanode in the first organic electrolyte includes soaking in a firstorganic electrolyte with A cations selected from a group consisting ofNa, Ka, Mg, and Ca; wherein accepting the first electric field includesaccepting the first electric field between the anode and a metal firstcounter electrode additional with the selected A cations; and, whereinforming the metal SEI layer includes additionally forming the anode froma composite with the selected A cations.